The present disclosure relates to a device for changing electrode caps of a welding unit, and to a welding method.
In car body engineering, on a production line or in a manufacturing plant individual car body parts are assembled and welded by way of a welding unit to form a car body. For this purpose, not only does the welding unit have to execute a large number of welding operations for one car body, but the welding unit also has to successively manufacture a number of car bodies which are to be processed one after another on the production line or in the manufacturing plant.
The problem with this is that on a production line the number of different vehicle models and the associated variants, such as convertible, notchback, fastback etc., is continuously increasing and all of these model types and model variants are manufactured in one manufacturing plant. This means that the car bodies run through the manufacturing plant in an arbitrary order and with a cycle sequence or time span in between that is as short as possible. Thus, it is possible for the sequence of welding operations to be carried out in each case, for example the sequence of welding spots, not to be defined. However, the same welding tools, in particular welding tongs, are used for all models.
The problem with this is also that, as the number of model variants increases, the number of welding operations for a welding tool and the variance of these welding operations also increase. In this case, the material combinations and the position of the welding spots on the car body to be manufactured in each case are different. In addition, each welding tool, such as in particular welding tongs, is equipped with a fixed electrode cap which has a fixed electrode diameter, wherein the diameter of the electrode cap and thus of the cap surface area is produced using corresponding electrode cap milling tools.
Since the overall sheet thickness varies for example from 1.4 mm to 6.0 mm and differences of 0.6 mm to 2.5 mm arise in the individual sheet thicknesses, the requirements placed on the cap surface area frequently come into conflict. For a material connection at the lower sheet thickness end a diameter of 4 mm and for a material connection at the upper sheet thickness end a diameter of 8 mm would be necessary for the electrode cap surface area. However, since the electrode cap surface area can be milled only with one diameter, a compromise has to be made in relation to the welds, such as welding spots, etc., to be produced. This influences the quality of the welds, such as welding spots, produced and the outlay which is required for production in order to ensure the quality of the welds. In addition, the time for manufacturing a car body should be as short as possible in order to optimize the throughput and thus the productivity of the production line or manufacturing plant.
Thus, the variance of the welding tasks in such manufacturing plants represents a major problem.